I. Field of the Invention
This invention relates generally to fire fighting apparatus, and more particularly to a system for introducing a liquid foam concentrate into a water stream in varying amounts to maintain a predetermined percentage mixture, irrespective of variations in the flow rate of the water stream where the system is automatically conditioned upon application of electrical power.
II. Discussion of the Prior Art
In our earlier U.S. Pat. No. Re. 35,362, the contents are which are hereby incorporated by reference, as if set out in full herein, there is described a system for controlling the introduction of a liquid chemical foamant into a water stream used in fighting fires at an appropriate flow rate so that the amount of foam in the water stream is of a predetermined concentration, irrespective of variations in the water flow rate. Identified in the ""362 patent as an xe2x80x9coptional enhancementxe2x80x9d is the inclusion of a compressed air source for projecting the foam/water mixture a greater distance as it exits a hose or water cannon. As described therein, it is important that the compressed air not be introduced into the water stream in the absence of the foam additive. Upon arriving at a fire, a human operator must start the introduction of the liquid chemical foamant by depressing an xe2x80x9con/offxe2x80x9d switch on the controller module. As is explained in the ""362 patent, upon depression of the on/off push button 32, the microprocessor in the controller module 26 executes an algorithm represented by the flow chart of FIG. 9 of that patent to control the introduction of foam concentrate into a water stream being pumped whereby the percentage concentration is maintained relatively constant irrespective of variations in the water flow rate as the fire fighter manipulates a hose nozzle.
It has been found advantageous to eliminate the need for a human operator to initiate operation. If either due to inattention or the excitement of the moment, a fire fighter should fail to depress the start button, air may be introduced in the water stream without the foam additive. Accordingly, it is a principal purpose of the present invention to provide a control feature that will assure that the system is in an auto-start condition at the time power is applied, obviating the need for a human operator to turn on the foam control system. The improvement to the prior art foam injection system described herein reduces the time needed to activate the foam injection system while providing all of the necessary safety interlocks to prevent untimely activation. Moreover, by implementing the present invention, only a single switch is needed in the cab of a fire-fighting vehicle thereby facilitating xe2x80x9cpump and rollxe2x80x9d operation of the vehicle when creating a fire brake when dealing with grass and brush fires.
The present invention provides in a fire fighting vehicle a system for introducing a liquid foam concentrate into a water stream in varying amounts to maintain a predetermined percentage mixture, irrespective of variations in water flow rates. The vehicle includes a source of electrical power for a water pump used to deliver raw water through a delivery hose. One or more foam pumps are used for delivering liquid foam concentrate from a supply tank carried by the vehicle into the delivery hose where it is mixed with raw water. Electric, hydraulic or both may be connected in driving relation to the foam pumps and a microprocessor-based controller, that is adapted to be energized from the source of electrical power, is coupled in controlling relation to the motor(s) that drives the foam pump(s) whereby the fluid flow output rate of the foam pump(s) can be varied. The present invention comprises an improvement to the above-described system. The microprocessor-based controller is programmed such that upon application of electrical power from the source to the microprocessor-based controller, the system is conditioned to introduce the liquid foam concentrate into the water stream by the foam pump(s) upon detection of raw water flow in the delivery hose. The auto start program executed by the microprocessor-based controller initially makes sure that the water pump and foam pump(s) are off and that they will be turned on only if predetermined conditions are met. Specifically, a test is made to determine whether the auto start mode is enabled and, if so, another test is made to determine whether the foam pumps are properly configured and the level of foam concentrate in the foam tank is above a predetermined level and then and only then will the software routine represented by the flow diagram of FIG. 9 of the aforereferenced Reissue U.S. Pat. No. 35,362 be called. Thus, the present invention conditions the system to inject foam concentrate into the water stream immediately upon detection that the water is being pumped and without the need for human intervention.